The present invention relates to an improved strap feeding and tensioning apparatus for use in a strapping machine for applying a strap around an object. More particularly, the present invention relates to a strap feeding and tensioning apparatus which is particularly adapted for use with steel or plastic strapping.
Prior art strapping machines are disclosed, for example, in U.S. Pat. No. 3,146,649, issued to E. Staron et al. on Sept. 1, 1964 and U.S. Pat. No. 3,768,397, issued to Robert F. Plattner on Oct. 30, 1973. These strapping machines, which are designed for use with steel strapping, typically include feeding and tensioning apparatus which includes a motor-driven feed wheel which cooperates with an idler feed wheel frictionally to grip the steel strapping therebetween, for moving the strap in feeding or tensioning directions, depending upon the direction of rotation of the drive wheel. To facilitate this gripping action, the drive wheel is provided with a plurality of gripping teeth or serrations. Another example of such a prior art strapping machine is manufactured by the assignee of the present invention under the designation "G9E Strapping Head", which is disclosed in an Interlake Instruction Manual for that machine, Form 1243R11-77. In this latter machine, the axis of rotation of the idler feed wheel is movable with respect to the axis of rotation of the drive wheel. A copy of this instruction manual, together with copies of the aforementioned prior art patents, are filed with this application, and they represent the most pertinent prior art of which applicant is aware.
But in these prior machines the amount of gripping force exerted on the strap by the drive and feed wheels has been limited to a predetermined range since forces in excess of that range cause the teeth or serrations on the drive wheel to score or penetrate the strapping, which could lead to severing of the strap under tension.
Yet, it is necessary to maintain considerable gripping force on the strapping, otherwise there will be a tendency for the strap to slip between the drive wheel and feed wheel as the tension in the strap is increased.